This invention relates generally to methods and compositions for applying a bioactive agent to a surface upon which enhanced bioeffect is desired.
Myriad fields benefit substantially from a bioactive agent-containing composition having a low viscosity which permits the use of conventional spraying equipment for application. For example, certain pesticides and herbicides which are employed in the protection of plant life are easily applied by spraying equipment. However, rapid run-off of the low viscosity material results in the need for a high frequency of spraying, with corresponding increase in cost, effort, and environmental damage. There is clearly a need for a delivery method which provides increased retention of the composition on protected surfaces such as the leaves of foliage.
A similar need exists for foods. For example, certain ingestibles can be protected with a coating which is conveniently applied in liquid form by spraying. The coating may reduce the effects of air on the ingestible substance through incorporation of protective bioactive agents, such as preservatives. These sprayable compositions, however, generally drain-off or are absorbed into such foods. The protective effect of the initial coating is thereby limited.
There is additionally a need for increasing the retention of bioactive agents which are commonly applied to surfaces of the bodies of living beings. They include, for example, various forms of therapeutic drugs, cosmetic agents, sun screens, insect repellents, etc. In many instances, it is desired that a liquid form of such materials be applied, especially by spray, and that the material be retained on the substrate to increase the duration of its effectiveness.
Of all these foregoing needs, by far the most complex problems relate to the administration for many drugs. Similarly, this is the field which has received the most attention. In most instances, however, the attention has been narrowly focused and incompletely successful.
For example, extensive research on the bioavailability of orally administered drugs indicates that there is a need to explore alternative modes of administration for many of them. First-pass metabolized drugs, for example, exhibit low bioavailability when administered orally. This result may be circumvented by nasal administration, with resultant absorption through the mucosa directly into the bloodstream. Nasal sprays are, therefore, an alternative route of administration for such bioactive agents.
A serious disadvantage of this form of administration is that the solutions tend to drain rapidly into the oral cavity, causing severe losses of drug. Such losses substantially reduce the bioavailability of a drug dose. There is therefore a need for a method for delivering drugs to the body of a living being, illustratively intranasally, wherein drainage of the drug is minimized.
Application by spraying a fluid containing a bioactive agent such as a therapeutic drug onto the desired site of application is an extremely convenient form of drug administration. Often there is a need, however, to prolong the residence time of a drug at a site of application so that the extent of drug absorption is elevated. Additionally, prolongation of the residence time is desired to increase the drug bioavailability and sustain the drug's action.
Another means for applying such drugs is in gels and/or ointments. Gels and ointments have the capacity to reside for a greater time at a site of application than a sprayable fluid. Gels and ointments, however, have three major disadvantages: inconvenience of use, particularly for chronic administration; inconsistency in the amount of drug applied in any given application and reduced area of contact. Thus, there is a need for a delivery method and bioactive composition which can be sprayed or otherwise applied to body cavities both consistently and easily using commercial mechanical systems.